The present invention relates to a device for integrated suspension and manipulation of the legs for supporting a platform for drilling or oil production at sea and relates more particularly to jack-up platforms.
Platforms of this type generally comprise legs which rest on the sea bed and a hull mounted so as to be displaceable and adjustable in height along the legs.
The whole platform is floated to the drilling or extraction site and the legs are lowered until they come into contact with the sea bed and then, resting on the legs, the hull is hoisted above the level of the sea to a height which puts it out of range of the highest waves.
The hull is thus displaceable along the legs of the platform by means of raising mechanisms integral with the hull and comprising output gears whose bearings are integral with the hull and co-operate with racks mounted on at least part of the length of the legs. These gears are motorized by a plurality of motors, for example electric motors, associated with speed reducers, the speed reducing ratio of which is very high.
At the moment of contact of a leg with the sea bed, at the end of the lowering operation, the impact can be very violent given the movements of the hull under the effect of a swell. These shocks reverberate in the raising mechanisms, severely stressing the multiple gearing of the speed reducers.
To obtain proper operation of the gearing of the speed reducers at the moment of contact of the legs with the sea bed, it is thus necessary to overdimension them significantly or to wait for favourable climatic conditions, thus increasing the costs of installation.
In order to remedy these disadvantages, a device for the suspension of the legs is known which consists of a turning balancing arm.
However, in this case the number of torsional turns of the balancing arm is limited, which reduces the damping travel, and the presence of this turning arm is dangerous for the personnel working on the platform.
FR-A-2 607 165 likewise discloses a device for the suspension of the legs of an oil platform which comprises at least one torsion bar, one of the ends of which is equipped with a gear meshing with a toothed sector mounted on the speed reducer and the other end of which is immobilized on the structure integral with the hull of the platform.
In this device, the torsion bar or bars are arranged parallel to the axis of rotation of the drive mechanism, increasing the size of the unit.